Conventional snowmobile drive trains incorporate a continuously variable transmission (CVT) having a driving pulley that is operatively coupled to the engine crankshaft and a driven pulley coupled to a driven shaft. The driving pulley acts as a clutch and includes a centrifugally actuated adjusting mechanism through which the drive ratio of the CVT is varied progressively as a function of the engine speed and the output torque at the driven pulley. Typically, the driven shaft is a transverse jackshaft which drives the input member of a chain and sprocket reduction drive. The output of reduction drive is coupled to one end of the axle on which are located the drive track drive sprocket wheels.
Although a centrifugal CVT provides many advantages, the fact that the drive ratio of the CVT is directly related to the engine speed causes some disadvantages. One such disadvantage is that the calibration of the driving pulley is always linked with the maximum power output of the engine. Although this results in great acceleration characteristics for the snowmobile, when the snowmobile operates at cruising speeds it results in the engine operating at a greater speed than necessary, high fuel consumption, high noise levels, and a lot of vibrations being transmitted to the riders of the snowmobile.
Representative of the art is US patent application no. 2011/0277577 which discloses a method of managing a transmission ratio with an assisted CVT with a governed engine to emulate a hydrostatic transmission and prevent a drivebelt abuse is provided, the method comprising: providing a reference power source rotational speed, using the assisted CVT to transmit rotatable motion between a power source and a drive mechanism, managing a torque of the power source to maintain a substantially even rotational speed upon a power source load variation and modulating a transmission ratio of the assisted CVT to change the rotational speed of the drive mechanism. A system and a vehicle having such a drivebelt abuse preventing mechanism is also provided.
What is needed is a CVT having a motorized controller actuating a movable sheave for adjusting a transmission ratio. The present invention meets this need.